1. Technical Field
The disclosure concerns plasma etch processing of a workpiece such as a semiconductor wafer, in which plasma ion density distribution is controlled.
2. Background Discussion
Generally, plasma reactors or chambers of identical or similar design may produce similar process results, although there may be differences in process results among the plasma reactors. The process results are affected by plasma ion density distribution over the workpiece or wafer being processed. In cases in which a plasma etch process is performed, plasma ion density distribution is reflected by depth or etch rate distribution on wafer surface. In cases in which a plasma deposition process is performed, plasma ion density distribution is reflected by thickness or deposition rate distribution on the wafer surface. In large manufacturing facilities, a set of two or more plasma reactors of identical design may be used to perform an etch process on many workpieces. In such cases, differences in etch rate distribution among the set of plasma reactors can be problematical. Such differences may be attributable to mechanical tolerances or other factors in the assembly of the set of plasma reactors.